[Stoves] "78% Efficient"

Thu May 7 13:24:39 CDT 2015

Dear Frank

Interesting question. The EPA has some strange test methods that are not really based on matching performance in use. They mace other methods that are extremely precise and accurate. There is a real mix.

The manufacturers of wood stoves have been complaining for years that the test was so divorced from actual use that there was no real correlation between lab tests (official tests) and performance in use. The new regulations are supposed to address this. If you recall the discussion a while ago about Alexander in Russia, he was complaining about the new test and the way it averaged the efficiency numbers.

There are two groups now: those who have compliant stoves (tested in the new way) and the rest.

It is not clear yet how close the new test is to typical use. The way measurements are made for PM is reasonable, I feel. The method is not utterly precise ‎because it uses a hood with volume and pitot tube velocity with compensations for temperature and pressure. When emissions are low, fixed flow systems have difficulty measuring anything.

The alternatives are carbon mass balance or chemical mass balance. The former is used by the EPA for vehicles and the latter is used by SeTAR methods.

The efficiency (as a heater) can be determined using the Siegert Formula which is a chemical mass balance approach with various iterations depending on the ‎data available.

If you look deep into the origin of that assumption of 78% efficient, it is used to set emissions rates. It is a bit difficult to explain in a short method but this might help.

In the Indian Standard 13152 which is a Chula test, there is an implied thermal efficiency, something the EPA has stated for various calculations. In the Indian test there is a chart of pot sizes that one selects from based on the firepower. If a stove has a firepower of 5 kW then it is assumed it can 'cook a pot' of a certain size. If it is 10 kW it is assumed it can cook a pot of twice the capacity.

Think about this for a moment: what does 'cook' mean?

It means adequately heat and service the cooking needs in a pot of that capacity.

If you make a stove with 5 kW and say that it can cook the pot of the 10 kW rating according to the chart.

Now, should the stove be tested with the larger or smaller pot specified in the 5 kW ‎column of the Standard?

The assumption in the test method is that no one will ever make a stove that is twice as efficient. So creating a stove that will cook the larger pot with the smaller power is not anticipated by the Standard.

You see? So creating a stove that will cook an 80 litre pot with a '20 litre' fire is unexpected.

So in the EPA methods there is in the background calculations some things to do with emissions and performance that are based on a 78% efficiency.

The ad was misusing the default number and, in my view, the logo of the EPA. I do not know the rules they have for the use of their logo. For SABS markings you have to pay per label.

‎The US uses a non-Siegert method that is also, at root, a chemical balance method that uses only the carbon (as I understand it). It gives a different answer from the European method because one can deal with condensing furnaces and the other can't.

Regards
Crispin

Dear Crispin,

I wonder how many more years it will take to do such a simple job.

Frank

Frank Shields
franke at cruzio.com

> On May 6, 2015, at 12:27 PM, Crispin Pemberton-Pigott <crispinpigott at outlook.com> wrote:
>
> Dear Friends of Efficiency
>
> Here is the “Ad of the month” from the Alliance for Green Heat
> <image001.png>
> The problem starts with the EPA having a ‘default’ estimated heating efficiency based on a fuel type. No one has any idea what the heating efficiency is, apparently. Even if there was a set of measurement that came to the 78% figure, that would only apply to the stoves measured, not future stoves that might work much better.
>
> Note the ‘firepower’ is based on the theoretical heat available from the fuel. Oh wait, there are two fuels listed but only one heat ‘input’.  Heat input means the heat that could be generated from the fuel burned, not the heat actually generated.
>
> So, there are all sorts of problems in the stove industry, not just the cooking stoves.
>
> Makers of compliant stoves are suing the EPA to speed up the implementation of new lower emissions limits. Makers of non-complaint stoves are suing the EPA to have the new limits delayed. Some states are ignoring the new regs, some are applying them.
>
> At least the test method is an improvement over the old one, though no one is yet claiming that the test predicts performance in the field. The main purpose of the testing is outdoor air quality.
>
> Regards
> Crispin
>
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